Resetable circuit breakers are widely used in electrical circuits to prevent current overloads, and in many applications it is desireable that the circuit breaker be as small as possible. A number of designs and configurations of small or mini circuit breakers have been proposed and such breakers utilize a wide variety of operating mechanisms. Typical circuit breakers of the afore described type are shown in U.S. Pat. Nos. 2,362,850; 3,932,829; 4,167,720 and 4,258,349.
Known small circuit breakers, necessarily, require that the electrical contacts be relatively close to each other, and it is common for these circuit breakers to utilize a pair of sets of contacts to provide multiple conductor protection, and the proximity of the contacts may permit arcing between opening contacts if means are not present to prevent such occurrences. For instance, it is very difficult for small circuit breakers to meet the requirements of Underwriter Laboratory's 1077 class A standards with respect to spacing between conductors to resist arcing. With small circuit breakers "creepage", i.e. the tendency for arcing across carbon deposits, and "clearance", i.e. the noninsulated spacing between conductors, are difficult to control due to dimensional limitations.
It is an object of the invention to provide a circuit breaker of concise configuration which is manually operable between open and closed circuit conditions and meets the Underwriter Laboratory's 1077 class A standards including those with respect to creepage and clearance.
A further object of the invention is to provide a concise circuit breaker utilizing a maunally operated actuator wherein the contact control mechanism employs an over-center linkage in conjunction with a bell crank lever to provide a positive operation of the position of the movable contacts of the circuit breaker.
An additional object of the invention is to provide a concise circuit breaker using a thermal actuator to sense excess current conditions wherein the circuit breaker employs a leaf spring mounted movable contact, and the movable contact sufficiently separates from its fixed contact to minimize arcing, even if the actuator is maintained in the closed position.
Another object of the invention is to provide a concise circuit breaker utilizing a pair of sets of movable and fixed contacts wherein the circuit breaker employs an insulated barrier between conductors, thermal actuators and the sets of contacts and arc creepage path extenders are employed to minimize arcing during contact separation and when the circuit breaker is in the open condition.
Yet another object of the invention is to provide a circuit breaker of concise configuration wherein the operating components are so configured, assembled and supported within the circuit breaker housing as to ensure consistent operation, simplify assembly, maximize the efficiency of component operation and meet Underwriter Laboratory's requirements and specifications.
An additional object of the invention is to provide a concise circuit breaker wherein selected moving components are formed of self-lubricating materials obviating the necessity to apply separate lubricants.
In the practice of the invention a concise circuit breaker in accord with the inventive concepts includes a synthetic plastic outer housing of a substantially rectangular configuration having an access side which will face outwardly when the circuit breaker is installed, and the inner side includes a plurality of terminals for connection to the circuit being controlled. Deflectable retaining fingers are defined on the exterior of the outer housing for maintaining the housing within a "snap-in" opening.
The circuit breaker inner housing is provided with a manually operated pivotal actuator on its access side which may be pivoted between circuit open and closed positions. An over-center linkage is pivotally mounted upon the actuator, and a bell crank lever spring operator is, in turn, mounted on the over-center linkage which transfers the mechanical movement of the actuator to a spring biased contact mounted upon the free end of a leaf spring whereby the movement of the actuator is transfered to the leaf spring for moving the leaf spring's contact into engagement with a fixed contact to close the controlled circuit.
The amount of current flowing through the circuit breaker conductors is monitered by a thermal actuator in the form of a combination bimetal and electrical resistance member wherein excessive current causes the bimetal actutor to be displaced, and such displacement is sensed by a lock lever which controls the position of the bell crank spring operator. Hence, when excessive current causes the thermal actuator to operate the lock lever the lock lever releases the bell crank operator to permit the electrical contacts to separate. Such contact separation occurs under excessive current conditions regardless of the position of the manually operated circuit breaker actuator.
The pivot axes of the manual actuator, over-center linkage and bell crank operator are parallel, and as stops defined on the housing limit the movement of the manual actuator between its circuit open and circuit closed conditions movement of the manual actuator from the circuit open to the circuit closed position causes the axis which pivotally mounts the over-center linkage to the manual actuator to pass through the plane containing the axes of the pivots of the manual actuator and bell crank contact spring operator thereby locking the three components in the "circuit closed" condition.
Preferably, the circuit breaker includes two sets of fixed and movable contacts whereby two circuits are simultaneously controlled by the manual actuator. The contact sets are separated by a dielectric barrier extending through the housing midway between its largest sides and each contact set is located on a opposite side of the barrier. Anti-arcing and anti-creep configurations are defined in the barrier sides adjacent the contacts, and openings defined in the barrier to receive operating components are configured to minimize arcing through the barrier.
Arcing is also minimized by utilizing a "short" leaf spring for supporting the movable contact of each set whereby the entire length of the leaf spring pairs is separated by the dielectric barrier. The contact leaf spring is of a generally U-configuration and includes a short leg which is attached to the contact arm terminal extension, and a long leg having a free end upon which the movable contact is mounted. The base interconnecting the legs is of an arcuate configuration to minimize localized spring flex stress, and the length of the spring long leg is, preferably, about one half, or less, the dimension of the housing transverse to the length of the manual actutor, over-center linkage and bell crank operator axes. This "short" length of the leaf spring upon which the movable contact is mounted permits the leaf spring and contact to be separated from the other leaf spring and contact throughout their entire configuration by the dielectric barrier and barrier openings are not adjacent the contact opening as might permit "arc over".
The long leg of the contact leaf spring is engaged by the bell crank operator and the use of the bell crank and the "short" contact supporting leaf spring permits full separation or opening of the contacts in the "trip free" mode even if the manual actuator is held in the "closed" condition.